Patent GB-145124-A (GB)
Title: Improvements in printing plate matrices and method of making the same
IPC: B41C3/06
Filed: 1919-03-20
Abstract: 145,124. Alexander, A. E., (Stokes, J. S.). March 20, 1919. Printing - surfaces; stereotype.-A matrix for making printing- plates consists of a body of fibrous material impregnated short of saturation with a phenolic condensation product, and a non-fibrous facing incapable of adhering to the type forme or printing plate on which the matrix is moulded. The matrix is subjected to heat and pressure while on the forme &c. to cause the phenolic condensation product to harden and set into an infusible state. An underlay may be used beneath the type forme during the moulding of the matrix so that the printing-plates obtained from the matrix will not require any " make-ready." The matrix may also be moulded with grooves or other indicating-means to act as guides in securing the matrix in the casting-box, thus determining the position of the printing-characters on the cast plate relative to the edges of the plate and thereby facilitating the correct positioning of the plate in the printing- press. In one form of matrix, the facing layer s of metal which may be of granular form or a thin sheet of lead or copper but is preferably a foil sheet a of an alloy of equal parts of tin and lead. The sheet a may be backed by a lead foil sheet b and a second alloy foil sheet c, the whole being rolled together. One or more sheets d of fibrous material, preferably blotting paper or matrix paper is impregnated, such as by painting, short of saturation with the phenolic condensation product, and is cemented to the under surface of the metal facing by means of a varnish composed of phenolic condensation product and barium sulphate. The fibre sheet d is then saturated with water, alcohol or other volatile liquid but preferably water, until it is soft, chloride of zinc or other suitable agent being preferably added to the water to cause the phenolic condensation product to harden more quickly under the subsequent heating and pressing operation. The sheet is then placed with the metal face in contact with a metal faced blanket f laid on the forme T and is pressed by rollers R acting through blankets g. The blanket f is then removed and the sheet again rolled with the metal face in direct contact with the forme which is heated to drive off the water from the sheet. The blankets g are then removed and the hollows in the back of the sheet filled in with a paste h, Fig. 5, of liquid phenolic condensation product and barium sulphate, or a phenolic condensation product in powder form with lampblack or carbon. One or more backing sheets i prepared similarly to the sheets d are then placed upon the matrix and the whole subjected to heat and pressure in a press P. The pressure is released for a short time to permit the escape of gases and is then reapplied until the matrix is set hard. Instead of a facing of metal the matrix may have a facing layer of phenolic condensation product which, before the moulding operation, is heated under pressure sufficiently to give it a smooth surface which will not adhere to the type forme. The indicating grooves referred to above may be made by means of adjustable members Y, Fig. 7, having knife edges y, y, two such members Y being used to form two pairs of grooves at rightangles. The matrix may be cut along the outer groove of each pair and the inner grooves indicate the position of the bars for clamping the matrix in the plate casting or moulding apparatus. Specification 6955/19 is referred to.